Metal alloy and its manufacturing process



July 1, 1958 i H. BIBRING 2,841,511

METAL ALLOY AND ITS MANUFACTURING PROCESS Filed Sept. 14, 1953 Fig- 2400 200 300 400 58c 600 700 Goo Sou 4on0 -lxillllLlllll United StatesPatent METAL ALLOY AND ITS MANUFACTURING PROCESS Herv Bibring, Mendon,France, assignor to Oflice National dEtudes et de RecherchesAeronautiques, Chatillon-sous-Bagneux, France Application September 14,1953, Serial No. 379,779 Claims priority, application France September16, 1952 20 Claims. (Cl. 148-2) The present invention relates to a metalalloy and to its manufacturing process.

Numerous metal alloys, containing cobalt, nickel, chromium, molybdenum,have been proposed for high temperature service, and attempts have beenmade to prevent the creep and oxidation thereof at high workingtemperatures.

These alloys have made it possible to develop techniques as regardscases where prolonged service is not indispensable, but have notcontributed to resolve the problems which arise in the construction ofapparatus comprising members enduring high temperature service over longperiods of time. After a few hundred hours, in fact, the creep ratio ofthese alloys increases rapidly, said members becoming unserviceable.

The explanation of this evolution, as generally admitted, is that theprecipitation having caused the structural hardening is carried on; thiscorresponds to the coalescence or globulation of the dispersed phase,and, perhaps, also to its crystallographic rearrangement.

Castrefractory alloys are also known, which present interestingmechanical properties as regards high temperature service, but theseshow dilatometrical anomalies at working temperatures, this prohibitingcertain applications and are liable to cause perturbations duringoperation.

The invention, in one of its objects, aims to provide a cast metal alloypresenting very small creep at high temperature, and which is constantin ratio, even afterv a very long time of service.

Another object of the invention is to provide a metal alloy in whichsuper-ageing phenomena will not appear, which is thus capable ofconstituting the material used for manufacturing operating membersassociated in mechanical assemblies designed for long high temperatureservice without replacement.

A further object of the invention is to provide an alloy devoid ofdilatometrical anomalies in the contemplated field of application.

It is also an object of the invention to prevent the appearance of anyundesirable fragile phases in the alloy, either prior to, or during itsutilization.

A still further object of the invention is to provide an alloy formed bythe combination of components which are currently available in industry.

It is another object of the invention to provide cast alloy havingexcellent pouring features and which, consequently, enables theproduction of cast pieces by the lost wax process. 1 1

It is another object of the invention to provide an alloy giving castpieces directly usable without mechanical treatment after the casting.

The invention also enables the production of an unoxidizable corrosionresisting alloycapable of a specular olish. p It is also an object ofthe invention to provide an alloy possessing good welding propertieswithout observing any special precautions, either as regardsauto-welding or as regards welding to other'metals or ferrous alloys.

The invention aims also at a process for the elaboration of an alloysuch as defined above.

The invention, in this respect, aims to provide a process which enablesthe production of pieces presenting good dimensional stability.

The alloy according to the invention, while utilizing the abovementioned structural hardening to the 'best advantage, using improvedmeans, hereinafter more fully described, utilizes also another hardeningprocess which, in essence, is not evolutive with time, the alloyacquiring thus high mechanical assistance properties at hightemperatures extending over a long period of time.

According to the invention, the hardening, instead of being caused bythe heterogeneousness introduced by the presence of a precipitate of adetermined phase into a matrix in a different phase, is caused also bythe heterogeneousness procured -by the simultaneous presence of twoallotropic forms of the same metal or same metallic compound, the changefrom one form to the other taking place without any transformation incomposition, and, accordingly, without diffusion through a martensitictype of mechanism, which is not dependent on the operational time ofservice.

In this respect, the alloy according to the invention is characterizedby the fact that it includes simultaneously and in a clearly definedproportion, in the vicinity of one by preference, cobalt, or a cobaltsolid solution on the one hand, in a face-centered cubic lattice crystalform, de-' nominated a form, or perhaps a stable modification of thelatter, and, on the other hand, in a compact hexagonal lattice form, or[3 form.

It is thought that the heterogeneousness, procured by the fineprecipitation of the B hexagonal form into the face-centered cubiclattice matrix a, through the martensitic type of mechanism, contributesto the good performance the alloy at high temperature, the precipitationof A the [3 form into the a type matrix causing a strained conditionwhich contributes to the hardening.

The alloy includes substances in proportions such that thetransformation from one form to the other, although sufficiently sloweddown, will lead, at the operating temperature, to a relative or type and13 type percentagesuch as will be most profitable, preferably of theabove mentioned value. 1

The cobalt-base alloy according to the invention comprises, as regardssubstances propitious for a structure formation, nickel, iron, carbon,and, as propitious substances for the 5 structure, chromium andmolybdenum.

According to the invention, the a-genous action of nitrogen, alwayspresent, and which would be dilficult to control, is avoided by thepresence of zirconium, with or without titanium. 1

The undesirable mutual reactions between the above mentioned substancesare also avoided by the addition of zirconium, with or without titanium.

The proportions in the above specified substances may be varied, butwithin very narrow limits, inorder to meet the various requirementsmentioned in the preceding paragraphs, and, also, owing to the fact thatseveral of these intervene in other manners in the alloy, as this willbe.

3 planes, enabling thus to pass from one crystalline system to another.

(b) The action is completed at the end of the elaboration stage, bysubjecting the alloy to a permanent deformation, under heat, whichcauses a partial change from the or form to the {3 form, this changeresulting in a relative proportion of oz and [3 of a stable nature,probably due to the appearance during the plastic deformation of astable modification of the a form. The alloy according to'the inventionretains a large grain dendritic appearance crystallization, this type ofstructure ensuring not only a better resistance to creep, but also, asproved by'tests,'exce1lent wear-resisting properties at high temperature(repeated alternating stresses);

The large grain dendritic segregation is developed by the fusiontechnique, by carefully selecting the casting and mould temperatures,and by adopting a composition such that the liquidus and the solidusareas will be sufliciently far apart. To retain this segregation, thealloy will not, theoretically, be subjected to any subsequent mechanicalworking or shaping.

The alloy according to the invention is also characterized by itsrelatively high. percentage of carbon, higher, theoretically, than 0.6%,by weight.

The presence of a relatively high percentage of carbon, reducing thecooling speed of the alloy and decreasing the first crystallizationtemperature, enables the results in a growth of the grains to proceedfaster than the solidification. This high percentage of carbon,moreover, ensures the absence of dilatometrical anomalies in the alloyby suppressing any changes in the course of heating, since it widens thestability zone of the oa'form, which is stable at high temperature.

It procures also a dense carburic pattern to the alloy, this beingpropitious to a good performance at high temperature.

The invention makes also provision for adding nickel in such proportionsthat it will not only play its part in helping to the formation of the astructure, but also,

owing to the increase of the solubility area of the Cr into the Co, itavoids the formation of hard and brittle compounds in the alloy, such asCo Cr in spite of the fact that the Co proportion is higher than 40%,and that a Cr proportion sufiicient for conferring good oxidationresisting properties to the alloy and for favouring the appearance ofthe 5 form.

According to the invention, the nickel percentage goes with pair with adependent carbon percentage, which compensates the effect resulting ofthe Ni addition as shown by the liquidus and solidus being broughtnearer to each other, the carbon and nickel being present, in this view,advantageously in equi-atomic quantities.

Zirconium and titanium, even in slight amounts, oppose to the'oxidationof the type known as catastrophic oxidation, which could be caused bythe presence of molyb denum.

Zirconium and titanium, moreover, stabilize the chromium and molybdenumpercentage in the matrix, in spite of the presence of a noticeableamount of carbon, since they show a greater affinity for this substancethan Cr and Mo.

Further, zirconium and titanium fix the nitrogen in the form of nitridesor cyanides, and prevent this element, always present, from acting in anuncontrollable manner on the stabilization of the or form.

which occurs at various temperaturesextending over a P wide scale and atdifferent moments covering a long period of time.

The mechanical properties of the alloy according to the invention arethus increased by a hardening process similar to the one utilized insome known types of alloys, but the hardening in the present case iscarried out in an extremely more efiicient manner with respect to theoperational time, and also with respect to the variety of the operatingtemperatures.

To this result contributes also the evolution dilferent relatively totime, and according to the various temperatures, of the differentintermetallic precipitates or carbides in which enter the elementsintroduced in the alloy, and, namely, chromium, molybdenum, carbon,zirconium and titanium.

The invention includes a series of alloys wherein the component elementspercentages are comprised within the following limits:

proportions ensuring remarkable high temperature creep properties wouldhave to be close to the following values:

Co 9 Cr 6 Mo 1 Ni l the C atomic proportion may vary within limits comprised between one half and one time that of Ni.

Changes may be made in the above given atomic proportions to meet anyparticular requirement. For instance, if it is desired that the alloy bepossessed with special oxidation resisting properties, the percentage ofcarbon will be decreased, whereas the proportion of the first fourelements will remain practically unchanged.

The carbon percentage may be reduced to 0.3%, the

loss of creep properties not being so important in this case.

An alloy of this type, having a small percentage of carbon, permitsnamely to cover large surfaces free of defects such as tears,contraction cracks or clinks.

If the alloy is to include tungsten, the atomic proportions must beproximate of the values given below:

Co 9 Cr Mo 1.5 W 0.75 Ni 2.5 C 1 EXAMPLE I The composition of the alloyis (percent by weight):

Co 50' Cr -a 28 Mo m. 10 Ni a- 6 C 1 Zr 01 Ti N 03 Si 1 Mn 1 Fe tocomplete Figure 1 shows the creep curve lot this alloy at 750 C. under astress of 18.1 kg./mm. and the-creep curves A and B of the twoforgednickelbase-alloys currently with an alloy according to the invention,the creep characteristics of the latter remaining unchanged respectivelyto time; the figure shows clearly that applying a pro-strain to nimonictype alloys (curves A and B) would refer to the useful part of the curveand, accordingly, would limit their service time.

By way of example, an elongation of approximately 0.35% (point M on thefigure) may be obtained under the conditions experimented andillustrated on curve I, (750 C. and 18.1 kg./mm. after 200 hours ofservice, but the alloy may, with advantage, be subjected to anequivalent deformation in a. much reduced time, by modifying theoperating conditions:

Thus an elongation of app. 0.4% is obtained:

In 10 hours at 790 C. with 18 kg./mm.

In 2 hours at 830 C. with 18 kg./mm.

In 35 mins. at 870 C. with 18 kg./mm. and also In mins. at 750 C. with42 kg./mm.

D on Figure 2, represents the differential dilatometrical curve on thealloy between and 1000 C. respectively to a Pyros test piece (curveobtained by means of a photo-recording Chevenard differentialdilatometer).

The true expansion of the alloy is obtained by adding the Pyros testpiece expansion to the differential expansion read on the curve for thesame temperature.

This curve D is perfectly reversible. The aspect of the curve does notchange, even following prolonged high temperature treatment.

The specific weight of the alloy at 20 C. is 8 g./cm.

The mean expansion factor is 18.2 X 10" between 20 and 900 C.

The electrical resistivity at 20 C. is 88 microhms cm./cm.

The alloy is non-magnetic.

The modulus of elasticity at 1000 C. is 14,480 kg./mm.

The fatigue limit, at 730 C., for an undulated stress between 2.5 andkg./mm. with a pulsation of 32 c./s.

is higher than 3 x 10" reversals.

A high temperature tensile strength test shows at 815 C.:

Breaking load: 44 kg./mm.

Limit of proportionality: 32 kg./mm.

Elongation: 14.2 kg./mm.

EXAMPLE II The alloy has the following composition (percent by weight).

6 This alloy possesses also excellent creep-properties. Curve II onFigure 3 shows the creep curve of this alloy at 730 C. with a stress of10.5 kg./mm.

Curve 1' represents the creep curve of the alloy given in Example Iunder the conditions defined above.

The alloy according to Example II shows also a very steady differentialdilatometrical curve. It is represented on Figure 2 by reference DEXAMPLE III The alloy composition is as follows (percent by weight): CoI 39 Cr 25 Mo 10 W 10 Ni 10 C 1 Zr 0.1 Ti 0.3 Si 1 Mn 1 Fe to completeThe creep curve of this alloy, drawn under the same conditions than forExample II, is shown in III, Figure 3.

Elaboration of the alloy The alloy is obtained by casting, and thefollowing Co, Ni, Mo, Cr, Zr, Ti, Mn, Si.

Carbon may be introduced in the form of carburized parent alloy, byconventional means. i a

When fusion is carried out by means of an induction furnace, it will beadvantageous to introduce the carbon by means of graphite, immediatelyafter the titanium.

The pouring is carried out at 1500 C. The alloy is poured in pre-heatedmoulds, a suitable temperature for this being from 800 to 1050 C.,depending on the desired grain size.

The alloy is maintained at the Working temperature for twenty-fourhours, in order to cause the structural hardening on one hand, and, onthe other hand, to facilitate the partial allotropic transformation froma to B.

The alloy is then permitted to cool slowly. Pieces obtained at thisstage present already very interesting high temperature mechanicalcharacteristics, and may be utilized as they are.

The remarkable properties of the alloy, however, may be furtherincreased by a high temperature deformation before being put intoservice. This prior strainmay take place with advantage with the pieceunder service conditions. If necessary, this prior strain will befollowed by a final truing-up operation.

In a modification, this prior deformation can be obtained rapidly bysubjecting the piece to more severe mechanical or thermal conditionsthan those met in the contemplated application, as mentioned in ExampleI.

When manufacturing a piece having a determined dimension of an alloyaccording to the invention, it may be cast with a dimension slightlysmaller than the dimension corresponding to service, the piece beingultimately subjected to the above definedtreatment so as to bring it tothe said predetermined dimension.

The alloy according to the invention has remarkable smelting properties,and it can be reliedupon for the precise fabrication of pieces havingvarious and complex shapes designed for long service operation at hightemperatures. Its fluent pouring, for instance, permits the fabrication,by means of a precision pouring process (lost-wax process), of a turbinewheel and blade assembly in one single piece, free from defects.

What is claimed is: i V

1. A cast refractory metal alloy having substantially the followingcomposition:

Percent Co 50 Cr 28 Mo 10 Ni 6 C 1 Zr ()1 Ti 03 Si Mn 1 Fe the remainder2. A cast refractory metal alloy having substantially the followingcomposition;

Percent Co 55 Cr 27 Mo 7 Ni C 1 Zr 0.2 Ti 0.2 Si 1 Mn 1 Fe the remainder3. A cast refractory metal alloy having substantially the followingcomposition:

Percent Co 39 Cr 25 Mo W 10 Ni 10 C 1 Zr 0.1 Ti 0 3 Si 1 Mn 1 Fe theremainder 4. A cast cobalt base refractory metal alloy containing byweight in excess of approximately 40% cobalt, from 20% to 35% chromium,from 5% to 20% molybdenum, from 0 to tungsten, from 3% to 15% nickel,from 0.6% to 1.2% carbon, from 0 to 0.5% titanium, from 0.05% to 0.3%zirconium, less than 3% of silicon and manganese and iron, said ironbeing present and constituting the remainder of said alloy, said cobaltbeing present in both the alpha and beta allotropic forms thereof.

5. A cast cobalt base refractory metal alloy as recited in claim 4 inwhich said carbon and said nickel are present in equi-molecularquantities.

6. A cast cobalt base refractory metal alloy as recited in claim 4 inwhich the cobalt, chromium, molybdenum, nickel and carbon atomicproportions are substantially 9:611:121.

7. A cast cobalt base refractory metal alloy as recited in claim 4 inwhich the atomic proportions of cobalt, chromium, molybdenum, tungsten,nickel and carbon are substantially 9:6.5:1.5:0.75:2.5:1.

8. A cast cobalt base refractory metal alloy as recited in claim 4 inwhich said alpha and said beta allotropic forms of cobalt are present inapproximately equal proportions.

9. A cast cobalt base refractory metal alloy containing by weight inexcess of approximately 40% cobalt, from to chromium, from 5% to 20%molybdenum, than 0 to 15 tungsten, from 3% to 15% nickel,

from 0.6% to 1.2% carbon, from 0 to 0.5% titanium, from 0.05 to 0.3%zirconium, less than 3% of silicon and manganese and iron, said ironbeing present and constituting the remainder of said alloy, said cobaltbeing present in both the alpha and beta allotropic forms thereof, saidalloy having been maintained at a temperatures between about 800 C. andabout 1050 C. for a prolonged period of time.

10. A cast cobalt base refractory metal alloy as recited in claim 9 inwhich said alloy is maintained at the said temperature for about 24hours.

11. A cast cobalt base refractory metal alloy as recited in claim 9 inwhich said heat-treated alloy is drawn about 0.35%.

12. A cast cobalt base refractory metal alloy as recited in claim 9 inwhich said alloy is drawn after the same is cast and during the coolingthereof.

13. A cast cobalt base refractory metal alloy as recited in claim 9 inwhich said alloy is drawn at a temperature of about 750 C. to about 870C.

14. A cast cobalt base refractory metal alloy as recited in claim 9 inwhich said heat-treated alloy is mechanically drawn to permanentlydeform the same.

15. A process of producing a cast cobalt base refractory metal alloycharacterized by small creep of constant ratio at high temperaturecomprising admixing in amounts by weight in excess of approximately 40%cobalt, from 20% to 35% chromium, from 5 to 20% molybdenum, from 0 to15% tungsten, from 3% to 15% nickel, from 0.6% to 1.2% carbon, from O to0.5% titanium, from 0.05 to 0.3% zirconium, less than 3% of silicon andmanganese and iron, said iron being present and constituting theremainder of said alloy, casting said mixture, and maintaining said castmixture at a temperature between about 800 C. and about 1050 C. for aprolonged period of time.

16. A process as recited in claim 15 in which said heat treated alloy isdrawn about 0.35% at a temperature of about 750 C. to about 870 C.

17. A process as recited in claim 15 in which said heat-treated alloy ismechanically drawn to permanently deform the same.

18. A process as recited in claim 15 in which said mixture is cast intopreheated molds and maintained at a temperature between about 800 C. andabout 1050 C. and in which said cast mixture is maintained in said moldsat said temperature for a prolonged period of time.

19. A process as recited in claim 18 in which said alloy is maintainedin said molds at said temperature for about 24 hours.

'20. A process as recited in claim 15 in which said heat-treated castalloy is mechanically drawn at a temperature of about 750 C. to about870 C.

References Cited in the file of this patent UNITED STATES PATENTS119,682 Yeilding Oct. 33, 1871 1,417,638 Sowers May 30, 1922 1,517,354Gillett Dec. 21, 1924 1,830,550 Kerekgyarto Nov. 3, 1931 2,090,044Hassenbrush Aug. 17, 1937 2,299,871 Baird Oct. 27, 1942 2,486,576 SavageNov. 1, 1949 2,515,775 Eprernian July 18, 1950 2,617,725 Owens Nov. 11,1952 2,684,299 Binder July 20, 1954 OTHER REFERENCES Materials andMethods, June 1946, page 1562. Journal of Metals, vol. 188, pages154-161, January 1950.

15. A PROCESS OF PRODUCING A CAST COBALT BASE REFRACTORY METAL ALLOYCHARACTERIZED BY SMALL CREEP OF CONSTANT RATIO AT HIGH TEMPERATURECOMPRISING ADMIXING IN AMOUNTS BY WEIGHT IN EXCESS OF APPROXIMATELY 40%COBALT, FROM 20% TO 35% CHROMIUM, FROM 5 TO 20% MOLYBDENUM, FROM 0 TO15% TUNGSTEN, FROM 3% TO 15% NICKEL, FROM 0.6% TO 1.2% CARBON, FROM 0 TO0.5% TITANIUM, FROM 0.05% TO 0.3% ZIRCONIUM, LESS THAN 3% OF SILICON ANDMANGANESE AND IRON, SAID IRON BEING PRESENT AND CONSTITUTING THEREMAINDER OF SAID ALLOY, CASTING SAID MIXTURE, AND MAINTAINING SAID CASTMIXTURE AST A TEMPERATURE BETWEEN ABOUT 800*C. AND ABOUT 1050*C. FOR APROLONGED PERIOD OF TIME.